Dissipative silencers are widely utilized devices, as explained in the Chapter 1. They are able to provide good attenuation performances over the broad band, especially if dissipative and reflective behaviour are combined together.
In order to model the dissipative action of these silencers, a typical approach consists of introducing high distributed and concentrated pressure losses in some regions of the system, rendered via acoustically equivalent schemes [3]. First, a very high friction coefficient (f=0.1 compared with the typical f=0.004-0.005) can be adopted for all the ducts adjoining the sound absorptive material. Second, adiabatic pressure losses can be introduced in the middle of all the ducts representing the cavity, by means of the adiabatic pressure loss boundary conditions described in [3], with a value of the resistance coefficient K equal to 50. Both the losses enable the dissipation of the incident acoustic energy to be accounted for as heat in the
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absorption lining. Obviously the sound absorptive features of the silencer, which depend on the lining thickness and properties, may be simulated approximately by a suitable combination of distributed and concentrated losses [3].
Chapter 2 – References
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R
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